Troubleshooting ProSeal LMA

Summary Supraglottic devices have changed the face of the airway management. These devices have contributed in a big way in airway management especially, in the difficult airway scenario significantly decreasing the pharyngolaryngeal morbidity. There is a plethora of these devices, which has been well matched by their wider acceptance in clinical practice. ProSeal laryngeal mask airway (PLMA) is one such frequently used device employed for spontaneous as well as controlled ventilation. However, the use of PLMAat times may be associated with certain problems. Some of the problems related with its use are unique while others are akin to the classic laryngeal mask airway (cLMA). However, expertise is needed for its safe and judicious use, correct placement, recognition and management of its various malpositions and complications. The present article describes the tests employed for proper confirmation of placementto assessthe ventilatoryand the drain tube functions of the mask, diagnosis of various malpositions and the management of these aspects. All these areas have been highlighted under the heading of troubleshooting PLMA. Many problems can be solved by proper patient and procedure selection, maintaining adequate depth of anaesthesia, diagnosis and management of malpositions. Proper fixation of the device and monitoring cuff pressure intraopera-tivelymay bringdown the incidence of airway morbidity.


Introduction
The ProSeal laryngealmask airway (PLMA) is the most complex and advanced version amongall the laryngeal mask airways (LMAs). 1,2 Some of the problems with its use are unique, such as oesophageal aspiration of air, gastric distension and airway obstruction which can occur even when the PLMA is correctly placed with a proper insertion technique. [3][4][5] The other problems encountered are akin to the classic laryngeal mask airway (cLMA), with varying degrees of frequency and intensity. As a routine after insertion and inflation of the PLMA cuff to 60 cm H 2 O, the correct placement of the device is confirmed by several observations and certain specific tests designated to assess PLMA positioningand evaluatethe ventilatoryand drain tube functions of the mask. These diagnostic tests are simple and quick to perform and the first five of the following are more popular. After confirmingcorrect positioning, the PLMA is properly secured to avoid dislodgement as its cuff is bulkier than that of the cLMA.

Visual assessment of depth of insertion
Assess for adequate depth of insertion by examining the relation of the integral bite block to the incisors. Ideally the bite block lies between the teeth but protrudes in case the PLMA is inadequately inserted. Stix and O'Connor in a study of 274 adults, found that when the ProSeal LMA was correctly positioned, the midway point of the bite block was proximal to the incisors in 78% of women and 92% of men.APLMA with its bite block lying entirely outside the mouth is almostunquestionably malpositioned. 6

Unobstructed inspiratory and expiratory flow
This is assessed by manually ventilatingthe patient, observingchest movements,capnography, expired tidal volume (V T ) of > 8 ml / kg, and evaluating the compliance by feelof the bag. The reported incidence of airway obstruction with PLMA has been found to vary from 2-10 %. 7,8 Increased resistance is suspected with partialobstruction resultingfrom infoldingof the PLMA cuffor downfoldingof epiglottis. 3 The PLMA, with its large drain tube and cuff, may produce respiratory obstruction by displacingthe cricoid cartilage anteriorly thereby exertingdirectpressure on the arytenoid bodies and muscular processes. 9

Suprasternal notch tap test or Brimacombe bounce
Th e su prasternal notch tap test or the "Brimacombe bounce"confirms the location of the PLMA tip in the oesophagus behind the cricoid cartilage. The test was first described by O'Connor et al in 2002. 10 It involves tapping the suprasternal notch or cricoid cartilage,and observingsimultaneous movement of a column of lubricant, or a soap bubble membrane at the proximal end of the drain tube. Both the structures lie in close proximity to the hypopharynx, where the correctly placed distalcuff sits. The drain tube must be patent for the test to be positive. The test works by cuffcompression causingdrain tubecompression within the drain tube,which in turn movesthe lubricantor soap bubble. O'Connor et al 10 reported a low false-negative rate for the suprasternalnotch tap test in 50 adults, but false positives and negatives can occur. False posi-tives can occur if the last 1-2 cm of the drain tube is folded over but some of the drain tube is still patent within the distal cuff. 11 False negatives can occur if the oesophagus is open, since this can weaken the pressure wave.

Gel Displacement Test
Water-soluble gel(0.5-1ml) isplaced at the proximalend of the drain tube so that it forms a column of about 2-3 cm. Minimal movement or gentle up and down movements indicates a normalposition. However, gelejection with gentle positive pressure ventilation (PPV), indicates a leak from the drain tube, signifyingimproper sealof devicewith thehypopharynx ( Fig  1). Thus, when positive, the test indicates airway leak through the drain tube. 1,2

Passage of gastric tube/ PVC catheter through drain tube to verify the patency of drain tube
The posterior folding of the masktip is ruled out by the successful passage of a gastric tube or a PVC catheter through the drain tube. 1,2,12

Soap Bubble Test
In this test, soap bubble solution is placed over the tipof the drain tube and followingobservations may be made. When the tip of the PLMA is in the laryngopharynx, soap bubble solution column bubbles or the soap membrane bursts during positive pressure ventilation. When the PLMA tip enters the glottis, the tracheobronchialtree communicatesdirectly to the drain tube. The drain tube transmits the airway pressures unless it is obstructed. The PLMA insertion into the glottis is diagnosedby watchingeither theformation of a spontaneous bubble which isblown away from drain tube port or the soap membrane oscillations seen with cardiac rhythm of the patient. 13,14

Thread test
A gauze thread or smallpiece of cotton held over the proximal end of a leaking drain tube can also be used to detect air leak from the drain tube. 13

Self-inflating bulb technique
This technique has been used for verification of proper placement of the oesophageal tracheal combitube®. 15 A self-inflating bagis attached to the drain tube,the bulb injects easilyand then remains collapsed with normal positioningof the PLMA. However, during glottic insertion, the self-inflatingbulb injects easily and then re-inflates. 16

Trachlight™
The Trachlight™ helps in quickly distinguishing glottic from oesophageallocationof thetip ofthe PLMA mask. Trachlight™ (Laerdal Medical, Wappingers Falls, NY, USA) after removing its stylet is passed through the drain tube just as for blind endotracheal intubation. 16 This is a simple and reliable means of detecting a PLMA tip foldover. 17 Adull glow in the anterior neck with passage of the Trachlight TM wand beyond the drain tube tip indicates correct alignment of the PLMAwith the upper esophagealsphincter.

MaximumMinute Volume Ventilation (MMV)
Th e MMV test consists of m anually hyperventilating ananaesthetized and paralyzed patient with a PLMA for 15 seconds and extrapolatingthe total exhaled volume to one minute which can be graded as follows. The test is easy to perform and can be completed with equipment that is readily accessible to almost every anaesthesiologist.
Anaesthesiologists should be alerted to the potential for significant airway obstruction in any patient with a MMV less than 12 L/min. It is advisable to remove the PLMA and use an alternative device before the initiation of surgery. 9 In this scenario, one should not have a false sense of security due to the normal oxygen saturation as the latter does not guarantee the satisfactory elimination of CO 2.
18 However, the decision to remove the PLMAshould be based depending on the patient's physical status, nature, site and duration of surgery.

Trouble Shooting
Problems related to the PLMA might occur during:i) insertion of the device ii)maintenance/ emergence phases of anaesthesia iii) recovery phase; in the post anaesthesia care unit or in the ward. Most of the problems are detected in the perioperative period but some airway morbidityand nerveinjuries mightcontinue even after the patient has been discharged from the hospital. Varioustools required for the purpose of trouble shootingare the PLMA itself with its cuff, drain tube and bite block, pressure gauge to monitor the oropharyngeal seal pressure, cuff pressure monitor, cotton, gauze thread, water soluble gel, and soap solution. Availability of respiratory module and fiberoptic scope can be very helpful in diagnosis and management of various malpositions. Common problems associated with PLMA use are:

I. Functional failure
This may result from several factors. The etiology could vary from failure to negotiatethe cuffthrough the oral cavity,various malpositionsto mechanicaland dynamic causes contributingto airwayobstruction inspite of a correctly placed device. 19

A. Device Insertion failure
The first-time and overallinsertion failure rate is 14% and 1% respectively. 19 This phase may be associated with problems such as difficulty in insertion due to the following reasons: (iii) Opening the patient's mouth with a laryngoscope followed by insertion of the device (iv) Gum elastic bougie / fiberoptic insertion, PVC / gastric tube as stents to stiffen the drain tube 12 (v) Deepening levelof anaesthesia (vi) Jaw thrust

B. Gastric tube insertion failure and gastric insufflation
The failure rate for gastric tube insertion is 4%. The mostcommon causesof failureof gastrictube placement are: 19 (i) Inadequate lubrication (ii) Selection of improper size (iii) Posterior folding of the mask (iv) Cooled gastric tube 22 The failure rate for prevention of gastric insufflation during PPV is 0.1% which is similar to the incidence seen with the tracheal tube. 19

C. Dislodgement with loss of airway during maintenance phase
The PLMA gets dislodged resultingin loss of airway duringthe maintenancephase dueto light plane of anaesthesia,improper fixation and changes in position e.g. extreme head down position during gynaecologic surgery and laparoscopic procedures. This can be avoided by proper fixation of the device. In the event of intraoperative displacement of the device, a gastric tube left in situ may be very helpfulin reinsertion of the device by simply railroading the drain tube over the gastric tube. 23

D. Malposition
Oneof themany advantages of PLMAover other LMA familymembers is that its malposition can be diagnosed and managed. 20,21 Slight malrotation is more common with the PLMA as compared to the cLMA probably because ofresidualrotation in thesagittalplane or distortion of glottic geometry. 24 Severalmalpositions have been described and the reported incidence is 5-15% at the first attempt. [19][20][21] The instruction manual describes three malpositions; 1,2 (i) insufficient insertion depth, (ii) PLMA insertion into the glottis, (iii)PLMA tip folded backwards behind the bowl against the posterior pharyngealwall.

. Distal cuff in laryngopharynx
When the PLMA is not inserted to the desired depth,the distalcuff sits in thelaryngopharaynx resulting in protrusion of the bite block. 2

Distal cuff in glottic inlet/PLMA insertion into the glottis
When the PLMA takes an anterior path during insertion, thedistal cuff collides with the glotticinlet and either remains there or falls back in the laryngopharynx.PLMA entry into the glottis isnot uncommonduringinsertion attempts because of the bulkyand flexible mask tip. When the PLMA enters the glottis then the drain tube acts as an extension of the tracheobronchial tree, airway pressuresaretherefore transmittedthrough the drain tube and not the airwaytube. 2,16 Diagnosis

Corrective measures
Correction usually requiresreinsertion usinga lat-eral approach, or the gum elastic bougie (GEB) technique. In majority of cases, the reinsertion of the mask is to a noticeably increaseddepth of insertion. Location of the PLMA tip in the oesophagus behind the cricoid cartilage can be confirmed usingthe "suprasternalnotch tap test." 10 To distinguish between inadequate depth of insertion and glottic impaction, the PLMA can be pushed further inwards:the former will usually be corrected while the latter made worse, with increased airwayobstruction orairway protectivereflex activation. 19 O'Connor and Stix have suggested that these malpositions canbe distinguished usingthesoap bubble test. 13,14

Distal cuff folded over
The advancingdistalcuff ofthe PLMA gets folded (Fig2) when it impacts against the posterior oropharyngealwall thereby obliterating the lumen of the drain tube. 19,20 Thus the distal cuff folds up beneath the advancingcuff untiltheunfoldedproximalcuffis redirected inferiorly into the laryngopharynxby thebuild up of the folded cuff in the oropharynx. The folded distal cuff cannot easily unfold as it gets wedged into the laryngopharynx. Foldingover has also been reported with the cLMA, 28 but is probably more common with the PLMA due to its soft backplate. 26 This malposition may occur with both finger / introducerinsertion and be associated with a better seal and higher mucosal pressures than the correctly placed PLMA.

Fig 2 Posterior folding of mask
Brimacombe et al, in a study of 95patients with the foldover malpositions, found that in92% resistance was encountered at the backof the mouth, in 83% the bite block protruded from the mouth, and in 98% ventilation was unaffected and the sealwas normal. 27 The main danger of unrecognisedfold overphenomenon is that it predisposes the patient to gastric insufflation, regurgitation and pulmonary aspiration as ventilation is unhindered due to easily achieved high airway pressures. 19 Thepatency of the draintube must be assessed in allpatients with the PLMA to exclude this malposition. In situationswhere passage of agastric tube is not required, the patency can be tested by non-invasively passing the gastric tube or a PVC suction catheter only tillthe end of the drain tube. (iv) Digital correction by sweepinga finger behind the cuff Of these, digitalcorrection appears to be the least effective. Folding over cannot occur with the GEB insertion and gastric tube guided techniques.

Severe epiglottic downfolding
A well known cause of mechanical airway obstruction is severe epiglottic downfoldingwhich occurs when the epiglottis is dragged inferiorlyby the cuff and completely covers the laryngealinlet (Fig3). It is diagnosed when the anterior surface of the epiglottis is visible from the airway tube on fiberscope examination. 7 Althougha degreeof downfoldingof epiglottishas been reported in 17 % of cases, 29 critical airway obstruction seldom occurs from a downfoldedepiglottis due to the design feature as the drain tube always suspends the epiglottis off the floor of the bowl. However, with cuff infolding (thetwo outside cuffs meet in themidline and the epiglottis cannot enter the bowl), a downfolded epiglottis becomes a riskfactor for airway obstruction because it is now forced directly on the arytenoids. 9 It may occur as a result of pre-insertion inflation of cuff, compression of pharynx and enlarged or floppy epiglottis.

Supraglottic and Glottic Compression
Glotticcompression occurs when the glottic inlet is mechanically compressed by the distalcuff reducing the tension of the vocal cords. 5 It is more likely to occur with a smallpharynx, over inflated cuff and when the distalcuff is pressed into the hypopharynx with extra force. 19 Compression of supraglottic and glottic structures may occasionally contribute to significant upper airway obstruction with a correctly placed tip of the cuff lying behind the cricoid cartilage. 9

Corrective measures 5,20,21
Reinsertion does not usually solve the problem.
(i) Airshould be withdrawn from the cuff (ii)Anteroposterior diameter of the pharynx increased by adopting thesniffingposition (iii)Applying jaw thrust

Cuff infolding
Cuffinfolding refersto inwardrotation ofthe large cuffs in front ofthe bowlso that they contact each other in the midline and obstruct gas flow (Fig4). It is relatively uncommon and Stix reported 2cases of cuff infolding out of 317 cases. 9,20 It is clinically indistinguishable from severe downfolding of epiglottis and both conditions may coexist at times. There is increased risk of cuff infolding with PLMA due to its deeper bowl and a more compliant cuff than that of the cLMA.  Table 1 shows Troubleshooting to various problems, causes, the required confirmatory test and their solutions.

II. Regurgitation and aspiration
Regurgitation of gastric contents may result in supracuff soilingof themaskandpulmonary aspiration with catastrophic results. 19,29 This may be precipitated by activationof protective reflexes due to lightplane of anaesthesia as greater depth of anaesthesia is required for insertion of PLMA as compared to cLMA. 30

Diagnosis
(i) Fluid seen in the airway /drain tube   6 • Take proper size PLMA, one size • Reflex glottic closure 7 smaller maybe tried for cuff infolding 5*, 6* •Ensure correct cuff inflation pressures 5*, 6* • Deepen anaesthesia or muscle relaxant 7* Many problems can be solved by proper patient and procedure selection, diagnosis and management of malpositions. Strategies to facilitate insertion by lateral/guided insertion techniques and maintaining adequate plane of anaesthesia may be helpfulin improvingfirst time and overall insertion success rates, correcting malpositions, overcoming difficult airway scenarios and prevention of regurgitation and pulmonary aspiration. Proper fixation of the device and monitoringcuff pressure intraoperatively especially during nitrous oxide based anaesthesia may bring down the incidence of airway morbidity.

CALENDER FOR AWARDS
Indian Society of Anaesthesiologists has instituted certain awards for its members every year. The eligible candidates have to submit the requirements to the SecretaryISA and some to the chairman of the scientific committee of ISACON 2009. The details of the awards and the procedures are available in our website www.isaweb.in.

Date
Towhom the Name of the Award application to be sent 30